I have a check engine light on but no ones computer can read it or turn on at all when hooked up to the connector. Any ideas? 99 jeep cherokee 4.0l

 

how many scan tools have you tried? do they report 0 codes or is there an error displayed on the scan tool? i'm wondering if the scan tool was faulty

 

http://www.go.jeep-xj.info/HowtoECUcodes.htm

 

Using the right tool?

 

Does your cigarette lighter work I was told to check that on my blazer because the light an port run off the same fuse

 

A lot is dependent on the quality of the scan tool as to what it will read. Check with a professional mechanic and have him check it for you with a better tool.

 

Waitaminute y'all. Does the ignition/light switch not suffice. I did it and it worked exactly as prescribed. Will a code tool say something different?

 

Yes i scanned it with my 150 scan tool and my friends 10,000 scan tool. Checking the wiring and grounds tomorrow.

 

Wheres the most common place to look at for a bad wire for these XJs though.

 

Checking wiring and grounds is absolutely a good place to start.

If multiple tools can't read the codes and you can't find anything with wiring or grounds, it's possible that you have experienced a computer failure.